The inventors of the present invention has proposed a technology of a recording/reproducing apparatus which uses SNDM (Scanning Nonlinear Dielectric Microscopy) for nanoscale analysis of a dielectric recording medium. In the SNDM, it is possible to increase resolution of measurement to sub-nanometer, by using an electrically conductive cantilever (or probe) having a small probe on its tip, which is used for atomic force microscopy (AFM) or the like. Recently, a super high-density recording/reproducing apparatus has been developed, wherein the apparatus records data into a recording medium having a recording layer made of a ferroelectric material by using the technology of SNDM (Japanese Patent Application Laying Open NO. 2003-085969).
In the recording/reproducing apparatus which uses the SNDM, the information is reproduced by detecting the positive or negative direction of the polarization in the recording medium. This is performed by using the fact that the oscillation frequency of an LC oscillator is changed due to a small capacitance change ΔC resulted from the inequality of a nonlinear dielectric constant caused by the distribution of the positive polarization and the negative polarization, wherein the LC oscillator includes a high-frequency feedback amplifier including an L component (inductance component), a conductive probe mounted thereon and a capacitance Cs of the ferroelectric material under the probe. In other words, the change of the distribution of the positive polarization and the negative polarization can be detected as an oscillation frequency change Δf.
Moreover, by applying an alternating electric field with a sufficiently low frequency to the oscillation frequency in order to detect a difference of the positive polarization and the negative polarization, the oscillation frequency is changed along with the alternating electric field. At the same time, a ratio of the change in the oscillation frequency including a plus-minus sign is determined depending on the nonlinear dielectric constant of the ferroelectric material under the probe.
Then, a component caused by the alternating electric field is FM (Frequency Modulation)-demodulated and extracted from a high-frequency signal of the LC oscillator which is FM-modulated in accordance with the small capacitance change ΔC along with the application of the alternating electric field, as described above. As a result, the record information recorded in the ferroelectric recording medium is reproduced.